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Malonic Ester Synthesis

Definition: What is Malonic Ester Synthesis?

Malonic ester is a diester molecule that can undergo hydrolysis to produce 1,3-dicarboxylic acid. The dicarboxylic acid, if gently heated, can undergo a decarboxylation reaction to produce carbon dioxide and an enol molecule. The enol then interconverts into a more stable carboxylic acid, like acetic acid.  This reaction is commonly known as malonic ester synthesis. This method conveniently allows the synthesis of mono- and disubstituted acetic acids, i.e., carboxylic acids bearing one or two alkyl groups on the α-carbon. The α-carbon on the malonic ester is relatively more acidic as compared to other esters. Alkylation at the alpha position can, therefore, be carried out with an alkyl halide (R-X) and relatively mild bases such as sodium hydroxide (NaOH) or sodium ethoxide (NaOEt) [1-7].

Malonic Ester Synthesis

Examples of Malonic Ester Synthesis

The most commonly used malonic ester is diethyl malonate, also known as diethyl propanedioate. This method can also be used to synthesize amino acids [1-6,8].

Malonic Ester Synthesis Example

Mechanism of Malonic Ester Synthesis

Malonic ester is an active methylene compound. The sequence of reactions is as follows [1-3,7]:

  1. Deprotonation of the ester to form an enolate
  2. Alkylation of an active methylene enolate
  3. Hydrolysis of the esters to a dicarboxylic acid
  4. Decarboxylation of a 1,3-dicarboxylic acid to give an enol which tautomerizes to α-alkyl carboxylic acid
Malonic Ester Synthesis Mechanism

Applications of Malonic Ester Synthesis

Malonic ester has been found useful in organic synthesis. For example, condensing urea with diethyl malonate produces barbituric acid. A large variety of barbiturate drugs is used for the treatment of insomnia and anxiety [9].

References:

  1. Definition, example, and mechanism – Chem.libretexts.org
  2. Definition, example, and mechanism – Chem.ucalgary.ca
  3. Definition, example, and mechanism – Uobabylon.edu.iq
  4. Definition and example – Chem.ucla.edu
  5. Definition and example – Ochempal.org
  6. Definition and example – Askthenerd.com
  7. Definition and mechanism – Pharmaxchange.info
  8. Examples – Organic-chemistry.org
  9. Applications – Onlinelibrary.wiley.com

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